Septa are barriers used to prevent contamination between a vessel's contents and the vessel's exterior environment. For example, to prevent contamination (e.g., degradation) of an oxygen- and/or moisture-sensitive material contained in a flask or a bottle, a septum in the form of a stopper can be used to seal the mouth of the flask or the bottle. The septum can also be used, for example, to seal a vessel containing a hazardous material, thereby preventing accidental spillage of the hazardous material.
Septa can include an elastomeric material (such as rubber) that can be repeatedly punctured by a needle or a cannula. When a septum is punctured, for example, by a needle, compressed elastomeric material can create a seal around the needle as the needle is used to transfer material (e.g., a fluid) into or out of a vessel. When the needle is withdrawn from the septum, the compressed material forces the puncture closed and reseals the vessel. As a result, material can be transferred into and out of the vessel with reduced or no substantial contamination.